1. Field of the Invention
The present invention relates to a GPRS (General Packet Radio Service) system and an in-zone node apparatus, and a bearer setting method used therefor, and in particular to a bearer setting method in the GPRS system.
2. Description of the Prior Art
The GPRS system is a mobile packet communication system for transferring data sent and received by data terminals, in a form of a packet without change even within a mobile communication network. With this system, it has become possible to provide even information having a real-time nature (e.g., voices, moving images), which mainly provided by circuit switching in the past, by introducing QoS (Quality of service) control satisfying service qualities (speed, delay, etc.) into a packet communication system.
As this QoS control, a PDP (Packet Data Protocol) context (PDP context) is established among an MS (Mobile Station), an RNC (Radio Network Controller), an SGSN (Serving GPRS Support Node) (in-zone node), and a GGSN (Gateway GPRS Support Node) (gateway node) which constitute the GPRS system. Note that the MS and the SGSN are connected by an RAN (Radio Access Network) and the SGSN and the GGSN are connected by a core network (backbone network).
Here, main functions of the SGSN include in-zone subscriber information management, in-zone subscriber movement management, outgoing and incoming call control, tunneling control, charging control, and QoS control. Main functions of the GGSN include ISP (Internet Services Provider) access management, address management, outgoing and incoming call control, tunneling control, charging control, and QoS control.
Concerning a procedure for the PDP context establishment in the present 3GPP (Third Generation Partnership Projects) standard, FIG. 8 shows a message flow in view of the QoS.
When this procedure for the PDP context establishment is examined from the standpoint of the SGSN, in order to guarantee the QoS required by the MS, both of a bearer between the MS and the SGSN and a bearer between the SGSN and GGSN have to be able to provide a frequency band width (Throughput) satisfying the QoS.
As shown in FIG. 8, in the procedure for the PDP context establishment in the present 3GPP standard, QoS negotiation between the SGSN and GGSN is carried out first, and based upon a result of the QoS negotiation, setting of an RAB (Radio Access Bearer) is carried out.
That is, when an activate PDP contest request (QoS: High) (e.g., speed of 2 Mbps) is sent from the MS (d1 in FIG. 8), the SGSN sends a create PDP context request (QoS: High) to the GGSN (d2 in FIG. 8).
However, a bearer satisfying “QoS: High” (speed of 2 Mbps) of this PDP context request cannot be secured in the GGSN, and if the bearer satisfying “QoS: Medium” (e.g., speed of 1 Mbps) (QoS Downgrade) is secured, the GGSN sends a create PDP context response (QoS: Medium) to the SGSN (d3 in FIG. 8).
Thus, the SGSN sends an RAB assignment request (QoS: Medium) to the RNC (d4 in FIG. 8). The RNC performs RAB setup between the RNC and the MS (d5 in FIG. 8).
In this case, if the QoS is downgraded due to a reason that the RAB cannot be secured sufficiently or the like in the RAB setup, the RNC sends an RAB assignment response (QoS: Low) (e.g., speed of 500 Kbps) to the SGSN (d6 in FIG. 8).
Therefore, the SGSN sends an update PDP context request (QoS: Low) to the GGSN (d7 in FIG. 8). Since the already secured QoS is downgraded in the GGSN, the QoS is not further downgraded, and the GGSN sends an update PDP context response (QoS: Low) to the SGSN (d8 in FIG. 8). Consequently, the bearer satisfying “QoS: Low” is secured as a route from the MS to the GGSN.
In the case in which the bearer satisfying the QoS cannot be provided between the MS and the SGSN as described above, the bearer between the SGSN and the GGSN is changed (reset) according to the downgraded QoS between the MS and the SGSN. According to this procedure, it becomes possible to make the QoS of the bearer provided between the MS and the SGSN and the QoS of the bearer provided between the SGSN and the GGSN to coincide with each other.
In the bearer setting method in the above-described conventional GPRS system, a secure QoS negotiation is made possible by the present procedure carrying out sequential bearer setting processing. Thus, it is likely that this sequential bearer setting processing becomes a factor of delay in PDP context establishment, and there is a problem in that smooth connection to the Internet from the MS becomes difficult.